about gyrotrons

Gyrotrons are powerful microwave sources, i.e. they emit electromagnetic waves at very high frequency and intensity. Typically, their output power is in order of hundreds of kW (one million times higher than a mobile phone emission power) and their frequency around one hundred GHz (a thousand times higher than the modern radio broadcasting frequency). This gyrotron frequency correspond to wavelength approx. 3 mm.

X2 gyrotron set-up
(compare with the scheme below and with the photograph of the X2 gyrotron on its page)

Coupling resonant electromagnetic microwaves to plasma is one of the most common methods of plasma heating (yes there is certain analogy to a microwave oven...). If the resonance condition is fulfilled, that means if the frequency of the microwaves excites one of the plasma proper frequencies, the waves can transfer their energy to plasma - which means they can heat the plasma.

A special case with the heating microwave frequency equal to the gyrofrequency of the plasma electrons (i.e. equal to the electron rotation frequency in the magnetic field which confines the plasma), or to its harmonics, is called Electron Cyclotron Resonance Heating (ECRH). And that's why gyrotrons are applied - their frequency correspond to frequency of significant ratio of electrons in hot plasmas of modern tokamaks.

Moreover, when the resonant electromagnetic wave has a component parallel to the field, it can support the electric current in the plasma (ECCD). For more details on ECRH and ECCD see our TCV webpage.

Gyrotron fundamentals

A gyrotron consists of an electron gun, an acceleration chamber, a resonance chamber (cavity) immersed in a strong magnetic field, and finally of a collector of electrons.

An electron beam is accelerated and introduced in a strong magnetic field generated by superconducting magnets.

Electrons are gyrating at high speed and start to emit an electromagnetic wave. It's frequency is therefore the gyration frequency of the electrons around the magnetic field lines (the gyro-frequency).

This frequency is matched to the resonance chamber where the relativistic electrons interact further with the electromagnetic field. The wave is thus strongly amplified, and is coupled out of the cavity to mirror systems from where the wave is guided to the target.

The decelerated electron beam reaches finally the collector, where the rest of energy is deposited.